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08-13-2008, 05:40 AM   #151
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QuoteOriginally posted by PentaxPoke Quote
Take some pictures and compare the edge sharpness to the center. Test at different apertures and focal lengths. If one edge is sharper than the other it is decentered (Bad). If the edges are all very "soft" compared to the center, again it is bad. My first copy of the lens had the first problem, my second had the second problem. Who knows what the third one will have... Often brick walls are used for this test since you have a uniform surface that you can easily discern the problem. My lens defects were so bad, I could see the problems without a brick wall. I have 2 other threads on this, in this forum.
How far from the wall should I take my test shots? Should I zoom full-in, full-out? Apperature ISO settings?

Thanks,
Victor

08-13-2008, 12:41 PM   #152
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QuoteOriginally posted by solarisdreams Quote
How far from the wall should I take my test shots? Should I zoom full-in, full-out? Apperature ISO settings?

Thanks,
Victor
All. Digital "film" is cheap.
08-13-2008, 04:52 PM   #153
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QuoteOriginally posted by solarisdreams Quote
How far from the wall should I take my test shots? Should I zoom full-in, full-out? Apperature ISO settings?

Thanks,
Victor
All of the above. I did my tests at 16, 20, 28, 35, and 50mm, at 2.8, 4.0, and 8.0, and at three different distances. Text-filled newspaper taped VERY FLAT to the wall can do it too. You want to take the first set as close to minimum focus distance as you can, and try to make each successive set at least a foot away. Use ISO100. Use a tripod. Use the 2-second timer to avoid mirror vibration.

As Poke pointed out, compare the center to the corners and edges. The corners will always be softer, especially at 2.8, but you should be able to tell if it is abnormally soft. Look for doubling, which my lens had at 28mm, but not at the extremes. Post pics with full-res crops of the center and corners if you're unsure.

Will
08-13-2008, 05:51 PM   #154
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Mine just arrived, I did newspaper tests and a series of candids at close range and a few landscapes. So far, the results are impressive at all focal lengths and 2.8 and outstanding at 5.6. One of the lenses that I handled at the B&H store had a hard zoom transition at 28mm where the second tube kicks in. This one is very smooth with a soft transition. A keeper. 90291xx

08-14-2008, 09:15 AM   #155
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Got my 16-50 from Japan again, did a brick wall test, making sure the lens was absolutely parallel to the wall by putting a small whiteboard in-between the wall and lens... last time, the copy I had was very soft on the right side... this time, I think both sides are equally soft. Can guys with good copies tell me if the softness exhibited here is the "normal" softness I would expect? Or should I go after Pentax once again?

All shot at 2.8 (I also shot at f4, f5.6 and f8. Improvements are noticeable, especially at 5.6 onwards, but not perfect...)

16mm


28mm


34mm


50mm


Is it just me or is the left side a little softer tan the right?

You can view the larger images at my flickr site, http://flickr.com/photos/thinkfloyd/

Thanks!
08-14-2008, 12:21 PM   #156
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I don't know how I didn't see this earlier but my 16-50 is way off kilter. Severely soft (OOF) on the left side. After noticing the trouble with the kids' golf camp photo I went home and took a series of shots at 16mm and 50mm for f/2.8, f/4.0, f/8.0 and f/16. No PP, just converted to JPG with ACR.

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08-14-2008, 07:24 PM   #157
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So I sent mine back today. It seems to have been well-centered, and was acceptably soft in the corners at 16mm and at 50mm. At 28 and near it, though, the corners were a mess and the lens even exhibited some doubling in those corners.

SN: 9027500
purchased at amazon

Will
08-14-2008, 08:30 PM   #158
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Holy you really screwed up this page for me with this big pics hehe. It's ok though.

I was thinking...when taking these test photos it should be important to set it on spot metering and center focus area (af point) right? I had some mixed results, some left soft some right soft and when I set it to spot metering and center focus, it was even. Is this correct? ...or should I leave both at multi?

08-14-2008, 10:51 PM   #159
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Welcome to the club Faither. That is clearly a decentering problem. Changing the lens focus method to "spot" or "auto" will have no effect. That would only affect wheather or not the picture is in focus. The problem is that only part of your picture is in focus, even though the subjects are at the same depth. That is decentering, and it is a manucacturing defect.

P.S. Please try to keep your picture widths in your posts a reasonable size. It has really thrown off the thread, so we have to scroll to the right to read.
08-15-2008, 09:06 AM   #160
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Sorry for the BIG photos. The lens is on its way back to Pentax. Fingers crossed on getting back a new lens as I'm just not sure how a lens so out of whack could be repaired.

JF
08-15-2008, 10:00 PM   #161
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Bought a 16-50mm lens, is it good?
All pictures are 80% resized.

f/2.8 iso 100 shake reduction off, tripod


100% crop, text is a little blurry, I just couldn't get it right.


f/2.8 1/50 iso 400 shake reduction on


100% crop


100% crop


f/2.8 1/8 iso 100, shake reduction off, tripod
soft on both sides
08-16-2008, 08:11 AM   #162
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Bad Copy

Bought the DA* 16-50 in Singapore 3 weeks ago, S/N 9023660 from the most reputable photo store there. A complete lemon.

Very soft wide open at wide focal lengths. Found SDM slow and very inaccurate - it wasn't obvious B/F or F/F - given enough time I could get focus dead on. This is with a K10, so it might have performed better with a K20, but it was next to useless, found myself constantly reverting to manual focus (I wonder whether this is why they designed the extra-wide focus ring?).

But it has quickly started to fall apart. The zoom ring has jammed completely, twice, the first time at around 35mm - it then mysteriously unjammed. It now won't zoom wider then 20mm, the barrel suddenly has quite a bit of play in it, more than my old 16-45, and there is a small part rattling around somewhere inside the lens.

There is nowhere in this region that can fix it - it will certainly have to go back to Japan. I hope Pentax will consider replacing it (it's under international warranty). I have never experienced this kind of quality problem with Pentax products in 26 years of using their products.
08-16-2008, 09:19 AM   #163
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Pak,

That is the worst experience I have heard yet with this lens. Sorry to hear that.

I am posting again for another reason: hopefully we can get to another page so we don't have to keep scrolling right because of those huge pictures!

How about a little help.
08-16-2008, 05:52 PM   #164
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QuoteOriginally posted by bjsmith Quote
Defective: 9029210
Purchased DA* 16-50 f/2.8 from Amazon.COM.
Absolutely sharp on the left, very nice, right out to the edges. But about 1/3rd into the right, resolution massively drops off and goes utterly soft.
It's far, far worse than my DA 16-45 f/4 on the right. Horrendously so.
Nominal: 9024998
Replacement DA* 16-50 f/2.8 from Amazon.COM
Not only the right, but even the center, is absolutely sharper than the prior sample.
In my preliminary shots, the very upper left looks a tad softer, but that may be a result of the prior sample being so sharp on the left, possibly inconsistently sharp in the upper left (the prior one possibly favoring it?).
In any case, it's a keeper.
08-16-2008, 08:37 PM   #165
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People, like I guess - do you plan to photograph brick walls and newspapers?
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